View Code of Problem 67

#include<stdio.h>
#include<math.h>
int main(){
	double x1,y1,x2,y2,x3,y3,x4,y4;
	double k1,k2,b1,b2;
	while(scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4)!=EOF){
		k1=(y2-y1)/(x2-x1);//算出两条直线的斜率 
		k2=(y4-y3)/(x4-x3);
		b1=y1-k1*x1;//算出两条直线的常数 
		b2=y3-k2*x2;
		if(x1==x2&&x3==x4) {
			if(x1==x3)
				printf("Yes\n");
			else 
				printf("No\n");
		} else {
			if(k1==k2&&b1!=b2)
				printf("No\n");//pingxing
			else
				printf("Yes\n");//xiangjiao
		}else{
			printf("Yes\n");
		}
	}
	return 0;
} 
/*
Main.c: In function 'main':
Main.c:21:4: error: 'else' without a previous 'if'
   }else{
    ^~~~
*/